Integrated photo detector, method of making the same

ABSTRACT

An integrated photo detector with enhanced electrostatic discharge damage (ESD) protection. The integrated photo detector includes a first photodiode formed in the SOI substrate and associated with a first p-electrode and a first n-electrode. Additionally, the integrated photo detector includes a second photodiode formed in the SOI substrate associated with a second p-electrode and a second n-electrode forming a capacitance no larger than a few femto Faradays. Moreover, the integrated photo detector includes a first electrode and a second electrode disposed respectively on the SOI substrate. The first/second electrode is respectively connected to the first p/n-electrode via a first/second metallic layer patterned with a reduced width from the first/second electrode to the first p/n-electrode and connected to the second p/n-electrode via a first/second metallic wire to make a parallel coupling between the first photodiode and the second photodiode with an ESD threshold of about 100V.

BACKGROUND OF THE INVENTION

The present invention relates to a high-speed optic-electrictelecommunication device. More particularly, the present inventionprovides an integrated photo detector with improved electrostaticdischarge damage threshold and a method of making the same.

Over the last few decades, the use of broadband communication networksexploded. In the early days Internet, popular applications were limitedto emails, bulletin board, and mostly informational and text-based webpage surfing, and the amount of data transferred was usually relativelysmall. Today, Internet and mobile applications demand a huge amount ofbandwidth for transferring photo, video, music, and other multimediafiles. For example, a social network like Facebook processes more than500 TB of data daily. With such high demands on data and data transfer,existing data communication systems need to be improved to address theseneeds.

As science and technology are updated rapidly, processing speed andcapacity of the computer increase correspondingly. The communicationtransmission or reception using the traditional cable is limited tobandwidth and transmission speed of the traditional cable and massinformation transmission required in modern life causes the traditionalcommunication replaces the traditional communication transmission systemgradually for systems requiring higher bandwidth and longer distancethat electrical cable cannot accommodate. With the advances of opticalcommunication technology and applications driven by the market demand onincreasing bandwidth and decreasing package footprint, more intensiveeffort and progress have been seen in the development of siliconphotonics on integrating electro-photonic circuits onsilicon-on-insulator (SOI) substrate for forming high-speedhigh-data-rate broadband optic-electric telecommunication devices.

In these broadband optical telecommunication devices based on siliconphotonics technology, Ge photodiode is commonly used as a photondetector for monitoring high-speed optical signal transmission since itcan be integrated onto silicon or SOI substrate monolithically. However,high-speed Ge photodiode is vulnerable to electrostatic discharge damage(ESD). Because of its low ESD threshold, many silicon photonicscommunication modules having Ge photo detectors suffered low assemblyyield. On the other hand, traditional ESD protection techniquesincluding schemes of using steering-diode arrays,transient-voltage-suppressor (TVS) diodes, and Zener diodes by externalchips are mostly geared for electronics module only but not for handlingphoto detection so as to not suit for being implemented into the siliconphotonics devices. FIG. 1 shows examples of conventional ESD protectioncircuit diagrams with Zener diodes. Each Zener diode (or a Zener diodepair) is used as an external chip for connecting in parallel (either inphase or out of phase) with a subject high-speed Ge photodiode (Ge PD).The Zener diode requires highly doped base region and is not regularlyformed in a same process for forming the Ge PD on the SOI substrate forhigh-speed optic-electric communication applications. Typically, forproviding ESD protection purpose, the Zener diode chip is formedseparately and mounted or connected to a photodiode chip by solder bumpor wire bonding, making the silicon photonics integration level muchlower and vulnerable to reliability and assembly yield issue.

Therefore, it is desired to develop improved photodiode devices/circuitswith improved ESD threshold for the integrated silicon photonicsdevices.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a high-speed optic-electrictelecommunication device. More particularly, the present inventionprovides an integrated photo detector with improved electrostaticdischarge damage threshold and a method of making the same. Merely byexample, the present invention discloses an integrated photodiodecircuit and a method for forming the same by coupling a Si photodiodewith a Ge photodiode in parallel with both being fabricated on a sameSOI substrate to provide high ESD threshold intrinsic to Si photodiodewhile maintaining high data rate in electrical signal converted by theGe photodiode, though other applications are possible.

In a specific embodiment, the present invention provides an integratedphoto detector with enhanced electrostatic discharge damage (ESD)protection. The integrated photo detector includes an input waveguideformed in a Si-on-insulator (SOI) substrate for receiving a light wave.The integrated photo detector additionally includes a first photodiodeformed in the SOI substrate and coupled to the input waveguide. Thefirst photodiode is associated with a first p-electrode and a firstn-electrode. Furthermore, the integrated photo detector includes asecond photodiode formed in the SOI substrate associated with a secondp-electrode and a second n-electrode forming a capacitance no largerthan a few femto Faradays. Moreover, the integrated photo detectorincludes a first electrode and a second electrode disposed respectivelyon the SOI substrate. The first/second electrode is respectivelyconnected to the first p/n-electrode via a first/second metallic layerpatterned with a reduced width from the first/second electrode to thefirst p/n-electrode and connected to the second p/n-electrode via afirst/second metallic wire.

In another specific embodiment, the present invention provides anintegrated photo detector with enhanced electrostatic discharge damage(ESD) protection. The integrated photo detector includes a Germaniumphotodiode comprising an intrinsic Germanium layer formed on a p-typeSilicon base layer patterned within a Si-on-Insulator (SOI) substrate.The intrinsic Germanium layer includes a first n++ doped region and thep-type Silicon base layer comprising a first p++ doped region.Additionally, the integrated photo detector includes a Siliconphotodiode comprising a Silicon region patterned within the SOIsubstrate to form a p-type Silicon portion joined with a n-type Siliconportion. The p-type Silicon portion includes a second p++ doped regionand the n-type Silicon portion comprising a second n++ doped region.Furthermore, the integrated photo detector includes a first metalliclayer being pattered to include a first p-electrode coupled to the firstp++ doped region, a second p-electrode coupled to the second p++ dopedregion, a first electrode connected to the first p-electrode by aportion of the first metallic layer with a reducing width and connectedto the second p-electrode by a first trace line. Moreover, theintegrated photo detector includes a second metallic layer beingpattered to include a first n-electrode coupled to the first n++ dopedregion, a second n-electrode coupled to the second n++ doped region, asecond electrode connected to the first n-electrode by a portion of thesecond metallic layer with a reducing width and connected to the secondn-electrode by a second trace line. The Silicon photodiode is coupledwith the Germanium photodiode electrically in parallel with acapacitance of no greater than a few femto Faradays and an enhanced ESDthreshold of about ±100V.

In another alternative embodiment, the present invention provides amethod for manufacturing an integrated photo detector with improvedelectrostatic discharge damage (ESD) protection. The method includesforming a first Silicon base block and a second Silicon base block on asubstrate. The method further includes forming a Germanium photodiodepartially in the first Silicon base block. The Germanium photodiode isassociated with a first p-electrode and a first n-electrode.Additionally, the method includes forming a Silicon photodiode in thesecond Silicon bask block. The Silicon photodiode is associated with asecond p-electrode and a second n-electrode. The second p-electrode andthe second n-electrode serve as two terminals of a capacitance no largerthan a few femto Faradays. The method further includes forming a firstelectrode and a second electrode separately on the substrate.Furthermore, the method includes forming a first metallic layer on thesubstrate. The first metallic layer is patterned to have a first portionwith a reducing width connecting the first electrode to the firstp-electrode and a second portion with a first trace line connecting thefirst electrode to the second p-electrode. Moreover, the method includesforming a second metallic layer on the substrate. The second metalliclayer is patterned to have a third portion with a reducing width toconnect the second electrode to the first n-electrode and a fourthportion with a second trace line to connect the second electrode to thesecond n-electrode.

Many benefits can be achieved with the present invention based onintegrating Ge PD with a Si PD in parallel on the same substrate. Thehigher ESD threshold of the added Si PD helps to improve the ESDprotection capability of the integrated photodiode. The smallcapacitance introduced by the added Si PD, which is in a few femtoFaradays range and is several orders of magnitudes lower than that of aconventional Zener diode for ESD protection, the enhanced ESD protectionby the added Si PD causes no impact on the high-speed performance of GePD. Additionally, Si-based and Ge-based PN junction photo diode can beeasily fabricated on SOI substrate in a unified process to form variousintegrated silicon photonics circuits.

The present invention achieves these benefits and others in the contextof known integrated silicon photonics devices. However, a furtherunderstanding of the nature and advantages of the present invention maybe realized by reference to the latter portions of the specification andattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following diagrams are merely examples, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize many other variations, modifications, and alternatives.It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this process andscope of the appended claims.

FIG. 1 shows examples of conventional ESD protection circuit diagramswith Zener diodes.

FIG. 2 is a simplified ESD protection circuit diagram according to anembodiment of the present invention.

FIG. 3 is a simplified diagram of an integrated photo detector havingboth Si PD and Ge PD fabricated on a same substrate according to anembodiment of the present invention.

FIG. 4 shows Human Body Model ESD test results of multiple samples witha single Ge PD only.

FIG. 5 shows Human Body Model ESD test results of multiple samples witha Ge PD being integrated in parallel with a Si PD according to anembodiment of the present invention.

FIG. 6A is a simplified diagram of an integrated photo detector havingboth Si PD and Ge PD fabricated on a same substrate according to anotherembodiment of the present invention.

FIG. 6B is a sectional view along AA′ across the Ge PD in FIG. 6A.

FIG. 6C is a sectional view along BB′ across the Si PD of FIG. 6A.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a high-speed optic-electrictelecommunication device. More particularly, the present inventionprovides an integrated photo detector with improved electrostaticdischarge damage threshold and a method of making the same. Merely byexample, the present invention discloses an integrated photo detectorand a method for forming the same by coupling a Si photodiode with a Gephotodiode in parallel fabricated on a same SOI substrate with an ESDthreshold of about 100V for high-speed data communication, though otherapplications are possible.

The following description is presented to enable one of ordinary skillin the art to make and use the invention and to incorporate it in thecontext of particular applications. Various modifications, as well as avariety of uses in different applications will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to a wide range of embodiments. Thus, the present inventionis not intended to be limited to the embodiments presented, but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

The reader's attention is directed to all papers and documents which arefiled concurrently with this specification and which are open to publicinspection with this specification, and the contents of all such papersand documents are incorporated herein by reference. All the featuresdisclosed in this specification, (including any accompanying claims,abstract, and drawings) may be replaced by alternative features servingthe same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

Furthermore, any element in a claim that does not explicitly state“means for” performing a specified function, or “step for” performing aspecific function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph 6. Inparticular, the use of “step of” or “act of” in the Claims herein is notintended to invoke the provisions of 35 U.S.C. 112, Paragraph 6.

Please note, if used, the labels left, right, front, back, top, bottom,forward, reverse, clockwise and counter clockwise have been used forconvenience purposes only and are not intended to imply any particularfixed direction. Instead, they are used to reflect relative locationsand/or directions between various portions of an object.

FIG. 2 is a simplified ESD protection circuit diagram according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. As shown, a Silicon photodiode (Si PD) is electricallyconnected with a Germanium photodiode (Ge PD) in parallel to form anintegrated photo detector with improved Electrostatic Discharge Damage(ESD) protection. In particular, the Si PD is connected the same phasewith the Ge PD, i.e., the p-nodes (or p-doped regions) of both the Si PDand the Ge PD are connected to one common node. The n-nodes (or n-dopedregions) of them are connected to another common node. Si PD inherentlyhas much lower dark current and much higher ESD threshold than Ge PD.Therefore, connection of Si PD with Ge PD in parallel will not impact GePD's leakage performance. The leakage performance is still limited tothe Ge PF within the integrated photo detector. Additionally, the Si PDadds just tiny capacitance in ˜fF level to the integrated photodetector. This ultra small extra capacitance does not impact high speedperformance of Ge PD as the integrated photo detector is implementedinto the silicon photonics integrated circuit for high-speedcommunication applications.

In an embodiment, the Si PD and the Ge PD are fabricated on the samesubstrate. For specific applications in silicon photonics devices,silicon-on-insulator (SOI) substrate is a preferred choice of thesubstrate. Si photodiode is a natural component on silicon photonicscircuit. Ge is similar to Si, though there is slight lattice mismatch.Ge PD has advantages in high-speed performance and can be formed by aprocess similar to the silicon process. Therefore, Ge PD becomes aleading candidate for integrating with a Si PD to form a high speedintegrated photo detector. FIG. 3 is a simplified diagram of anintegrated photo detector having both Si PD and Ge PD fabricated on asame substrate according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown, a high-speedintegrated photo detector 300 is fabricated on a substrate 301 byintegrating a high-speed Ge PD 310 with a Si PD 320 electrically inparallel. In particular, the Ge PD 310 includes a PN junction and has afirst p-electrode 310 a coupled to a p-type doped region of the Ge PD310 and a second n-electrode 310 b coupled to an n-type doped region ofthe Ge PD 310. Similarly, the Si PD 320 also has a second p-electrode320 a coupled to a p-type doped region of the Si PD 320 and a secondn-electrode 320 b coupled to an n-type doped region of the Si PD 320.Both the first p-electrode 310 a and the first n-electrode 310 b serveas two terminals of a first capacitor associated with the Ge PD 310.Both the second p-electrode 320 a and the second n-electrode 320 b serveas two terminals of a second capacitor associated with the Si PD 320.The sizes of the second p-electrode 320 a and the second n-electrode 320b are make small relative to those of the first p-electrode 310 a andthe first n-electrode 310 b to keep capacitance of the second capacitorsmall. In a specific embodiment, the capacitance of the second capacitorassociated with the Si PD 320 is kept no more than a few femto Faradays.This is to minimize its impact on the photo detection by the Ge PD 310.

In some embodiments, the integrated photo detector 300 includes a firstelectrode 315 and a second electrode 316, respectively disposed on thesubstrate 301 on two separate locations. In an embodiment, the firstelectrode 315 and the second electrode 316 are formed with a relativelarge size with a dimension of a few 10 s and 100 s micrometerssufficient for forming a solder bump for bounding wires to connect withan external electronic circuit (for telecommunication). In anotherembodiment, the first electrode 315 serves as a cathode and the secondelectrode 316 serves as an anode, for outputting electric signalsconverted from optical signals carried by a light wave detected by theGe PD 310. Optionally, the light wave is pre-modulated with a high datarate (such as 40 Gbit/s) and correspondingly the Ge PD 310 is able todetect the optical signal with high speed and convert to an electricsignal that maintains the high data rate. In yet another embodiment, thefirst electrode 315 is physically connected to the first p-electrode 310a and the second p-electrode 320 a, the second electrode 316 isphysically connected to the first n-electrode 310 b and the secondn-electrode 320 b, for coupling the Si PD 320 to the Ge PD 310electrically in parallel for enhancing Electrostatic Discharge Damageprotection.

In an embodiment, the integrated photo detector includes an inputwaveguide 305 fabricated in the same substrate 301. The Ge PD 310 isdirectly coupled with the input waveguide 305 for receiving the lightwave that carries high data rate optical signals. This input waveguide305 can be made by one material of Silicon, Germanium, Silicon Nitride,or other Silicon compound. The input waveguide 305, of course, is ableto connect with a light source, a modulator, and optionally amultiplexer/demultiplexer or other optical network components in anopto-electric communication system. It is merely an example of anopto-electronic device using a Ge PD for monitoring or measuring opticalpower associated with a plurality of silicon photonics circuits forhigh-speed telecommunication applications.

In some other embodiments, part or all of the first electrode 315, firstp-electrode 310 a, second p-electrode 320 a are formed by a singleprocess of forming a metallic layer overlying the substrate 301including the Ge PD 310 and the Si PD 320 and patterning it to separateelectrodes. Alternatively, part or all of the first electrode 316, firstn-electrode 310 b, second n-electrode 320 b are formed by a singleprocess of forming a metallic layer overlying the substrate 301including the Ge PD 310 and the Si PD 320 and patterning it to separateelectrodes. In an embodiment, all those electrodes are formed by asingle metalization process that includes optionally patterning,masking, depositing, or etching a certain thickness of a metallic layeroverlying partially the substrate 301, the Ge PD 310, and the Si PD 320.The metallic layer can be used commonly from copper, aluminum, tin,lead, or other good conductor material such as conductive oxides.

Referring to FIG. 3, a first metallic layer mentioned in last sectioncan be patterned to have a first portion 351 configured with reducingwidth to connect the first electrode 315 to the first p-electrode 310 aand a second portion 352 configured as a thin trace line to connect thefirst electrode 315 to the second p-electrode 320 a. Similarly, a secondmetallic layer is patterned to have a third portion 361 configured withreducing width to connect the second electrode 316 to the firstn-electrode 310 b and have a fourth portion 362 configured as a thintrace line to connect the second electrode 316 to the second n-electrode320 b.

The thin trace line 352/362 is part of the first/second metallic layersufficient for make the electrical conduction between the first/secondelectrode to the second p/n-electrode 320 a/320 b of the Si PD 320 butmade with a width as small as a few micrometers or less so that itcontributes negligible capacitance to the Si PD 320. Overall, providedwith a small size for each of the second p/n-electrode 320 a/320 b and asmall Si PD base block combining p-type doped region and n-type dopedregion, the Si PD 320 adds an ultra small (e.g., a few femto Faradays)capacitance to the integrated photo detector 300. This ultra smallcapacitance causes substantially no impact on the high-speed photondetection involved with the Ge PD 310. While in the conventionalapproach of using Zener diode for ESD protection, the capacitance ofZener is several order of magnitudes larger in pico Faradays range. Thatis at least one reason why Zener diode is not suitable for supportinghigh-speed optical telecommunication applications.

For any semiconductor devices with ESD protection circuitry, it isrequired to ensure their effectiveness and reliability to meetindustrial standards. Various kinds ESD test schemes are selected toperform and qualify the circuitry. For example, a human-body-model (HBM)scheme simulates ESD due to discharge from human beings. People areconsidered a principal source of ESD, and HBM is a commonly used modelto describe an ESD event. FIG. 4 shows HBM ESD test results of multiplesamples with a single Ge PD only. As shown, diode leakage dark currentdata collected for total seven samples with single Ge PD are plotted.Two of the seven samples are held as control samples under a fixedESD-free condition. Rest five samples are subjected to different ESDtest conditions including −50V test voltage, +50V test voltage, and±100V test voltages. It is shown that almost all samples show at least10 times increase in leakage dark current after −50V and +50V ESD test,setting a basis for demanding an improved high-speed photodiode withimproved ESD protection performance. A rough estimate of the ESDthreshold for the single Ge PD is barely ±50V (at least under HBM ESDtest scheme).

FIG. 5 shows HBM ESD test results of multiple samples with a Ge PD beingintegrated in parallel with a Si PD according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Asshown, diode leakage dark current data collected for total seven sampleswith Ge PD integrated with Si PD in parallel (see FIG. 2 and FIG. 3) areprovided. Two of the seven samples are held as control samples under afixed ESD-free condition. Five other samples are tested and measured thecorresponding leakage dark current under −50V, +50V, and ±100V ESD testvoltages. The data in FIG. 5 indicate that the leakage dark currentsubstantially stays in the same level after carrying out −50V and +50VESD tests due to enhanced protection introduced by the Si PD in theintegrated photodiode 300 (see FIG. 3). Only after the ESD test voltageincreases to ±100V should one see significant increase in the leakagedark current passing the integrated photodiode. A rough estimate of theESD threshold is about ±100V for the integrated photodiode having a GePD connected to a Si PD in parallel, which improves by 2 times over thatfor single Ge PD.

FIG. 6A is a simplified diagram of an integrated photo detector havingboth Si PD and Ge PD fabricated on a same substrate according to anotherembodiment of the present invention. As shown, a Ge PD 610 and a Si PD620 are fabricated on a single substrate 601. The substrate 601 is aSi-on-insulator (SOI) substrate having a silicon layer over a BOXinsulator layer on a silicon wafer substrate. Referring to FIG. 6A, theGe PD 610 includes a silicon base block 611 formed by patterning thesilicon layer of the SOI substrate 601 into a finite dimension. A dopingprocess can be performed to make the silicon base block 611 a p-typedoping characteristics. The doping process can be performed using animplant mask to dope the above region only. On the silicon base block611, a Germanium layer 613 can be formed by depositing intrinsic Gesubstantially free of doping impurities. Although there is a latticemismatch between Ge and Si, a certain thickness of strained Ge layer canbe formed. Optionally, Ge—Si alloy may be formed during the process.

In some embodiments, on the silicon base block 611, a doping process canbe carried to form a p++ doped region 612 in part of the silicon baseblock 611. Optionally, the p++ doped region 612 is formed on one part ofthe silicon base block 611. Optionally, the p++ doped region 612 isformed on two parts of the silicon base block 611 separated by theintrinsic Ge layer 613. Further, another doping process can be carriedto form a n++ doped region 614 within the intrinsic Ge layer 613. Allthe doping processes can be performed by using masked implantations withcorresponding p and n-type impurities. The depth of the p++ doped region612 can be as deep as the whole thickness of the silicon base block 611.The depth of the n++ doped region 614 is controlled to be less thantotal thickness of the intrinsic Ge layer 613. As a result, a PINjunction is formed as a core structure of the Ge PD 610 with a p-node atthe p++ doped region 612 in the silicon base block 611, an intrinsicregion at the intrinsic Ge layer 613, and an n-node at the n++ dopedregion 614. Furthermore, a p-electrode 610 a can be formed overlying atleast partial top of the p-node of the PIN junction and an n-electrode610 b can be formed on top of the n-node of the PIN junction. Thestructure of the Ge PD 610 is further illustrated in FIG. 6B in a crosssectional view along a cut line AA′ of FIG. 6A.

Referring to FIG. 6A again, the Si PD 620 is also formed by patterningthe original silicon layer of the SOI substrate 601 to a finite size andperforming masked implantation to obtain a base block containing ap-type doped region 621 joined with a n-type doped region 622.Optionally, the bask block for the Si PD 620 is made smaller relative tothe silicon base block 611 for the Ge PD 610. Optionally, another dopingprocess can be performed using masked implantation to form a p++ dopedregion 623 within the p-type doped region 621 and separately form an n++doped region 624 within the n-type doped region 622. As a result, a PNjunction is formed as a core structure for the Si PD 620 with a p-nodeat the p++ doped region 623 and an n-node at the n++ doped region 624.Furthermore, a p-electrode 620 a can be formed overlying at leastpartial top of the p-node of the PN junction and an n-electrode 620 bcan be formed on top of the n-node of the PN junction. The structure ofthe Si PD 620 is further illustrated in FIG. 6C in a cross sectionalview along a cut line BB′ of FIG. 6A.

In an alternative embodiment, a method for manufacturing an integratedphoto detector with enhanced electrostatic discharge damage (ESD)protection is provided and specifically shown below by referring to FIG.3 and FIGS. 6A, 6B, and 6C. The method includes forming a Germaniumphotodiode on a substrate, for example, on a Silicon wafer substrate ora silicon-on-insulator (SOI) substrate. SOI substrate is often used forforming integrated opto-electronics devices including photodiodes,planar waveguides, metallic electrodes, etc. The Germanium photodiode,as processed via a series of patterning, doping, depositing, masking,implanting, or etching steps within the SOI substrate, is configured tobe a PIN junction device associated with a first p-electrode separatedwith a first n-electrode by an intrinsic region.

Additionally, the method includes forming a Silicon photodiode on thesame substrate. The Silicon photodiode is configured, under asubstantially similar patterning, masking, implanting, or etchingprocess together with the formation of the Germanium photodiode over theSOI substrate, to be a PN junction device associated with a secondp-electrode and a second n-electrode. Both the second p-electrode andthe second n-electrode are made substantially smaller than the firstp-electrode and the first n-electrode to provide an ultra smallcapacitance in a few femto Faradays so that its impact on the Gephotodiode is minimized.

Furthermore, the method includes forming a first electrode and a secondelectrode separately on the SOI substrate respectively at two separatelocations away from the Ge PD and the Si PD. Optionally, the firstelectrode and the second electrode are made relatively larger than thep-electrode or n-electrode in either the Ge PD or Si PD. In an example,the first electrode and the second electrode has a lateral dimension ofa few tens or hundreds of micrometers. This size is sufficiently largefor forming solder bump for making conductive wire connection. Moreover,the method is using a first metallic layer patterned to have a firstportion with reducing width to connect the first electrode to the firstp-electrode in the Ge PD and a second portion with a thin trace line toconnect the first electrode to the second p-electrode in the Si PD.Similarly, the method is using a second metallic layer patterned to havea third portion with reducing width to connect the second electrode tothe first n-electrode in the Ge PD and a fourth portion with a thintrace line to connect the second electrode to the second n-electrode inthe Si PD.

Optionally, the first metallic layer and the second metallic layer is asame metal layer formed on the SOI substrate (including the as-formed GePD and Si PD) then patterned to have corresponding portions forconnecting respective electrodes. Optionally, the thin trace line ismade substantially small width of a few micrometers or less tominimizing its contribution to the ultra-small capacitance associatedwith the Si PD. These connections cause the Si PD to be coupled to theGe PD electrically in parallel, i.e., the first p-electrode of the Ge PDis connected to the second p-electrode of the Si PD and the firstn-electrode of the Ge PD is connected to the second n-electrode of theSi PD. The parallel connection of Si PD to the Ge PD provides anenhanced ESD protection to the integrated photo detector as the Si PDpossesses a higher ESD threshold inherently. At the same time, the Si PDhas lower dark current so as not to impact the Ge PD leakageperformance. The ultra-small capacitance of the Si PD keeps thehigh-speed performance of the Ge PD for converting light wave toelectrical signal.

Optionally, the PIN junction of the Ge PD includes a first Si base blockformed in the silicon layer of the SOI substrate. The first Si baseblock can be formed by masking and etching from the silicon layer to afinite lateral dimension depending on the design of the Ge PD. The firstSi base block is further doped to have a p-type characteristic byimplanting a p-type impurity into the block. Furthermore, the PINjunction includes an intrinsic Ge layer formed on a partial top portionof the (p-type) first Si base block by masking and depositing up to acertain thickness with strain due to slight lattice mismatch between Siand Ge. Moreover, the PIN junction includes additional doping process toform a first p++ doped region within the p-type Si base block and afirst n++ doped region within the intrinsic Ge layer. Optionally, thedoping process is performed using masked implantation. Optionally, adepth of the first p++ doped region is not specifically limited but canbe extended to a total thickness of the p-type Si base block. But, adepth of the first n++ doped region is limited to only partial thicknessof the intrinsic Ge layer leaving a finite gap of the intrinsic Gematerial above the p-type Si base block. Optionally, the first p++ dopedregion can be formed on two sides of the p-type first Si base blockseparated by the partial portion covered by the intrinsic Ge layer.Optionally, the first p++ doped region is formed on a single portion ofthe first Si base block.

Optionally, the first p-electrode is formed to directly couple with thefirst p++ doped region(s) of the PIN junction of the Ge PD and the firstn-electrode is formed to directly couple with the first n++ dopedregion.

Optionally, the PN junction of the Si PD includes a second Si base blockformed similarly in the SOI substrate by patterning, etching or otherprocesses to have a finite lateral dimension that is smaller than thefirst Si base block. The second Si base block is separated from thefirst Si base block. Further the second Si base block is performed adoping process to have a p-type portion joined with an n-type portion.Furthermore, the PN junction is formed by performing another dopingprocess to implant more p-type impurity into a partial region of thep-type portion to form a second p++ doped region and implant more n-typeimpurities into a partial region of the n-type portion to form a secondn++ doped region. Optionally, a depth of the second p++ doped region orthe second n++ doped region is not specifically limited but can beextended to a total thickness of the second Si base block.

Optionally, the second p-electrode is formed to directly couple with thesecond p++ doped region(s) of the PIN junction of the Ge PD and thesecond n-electrode is formed to directly couple with the second n++doped region.

Optionally, the method includes forming an input waveguide coupled tothe Ge PD for receiving a light wave that carries an optical signalmodulated with high data rate. The high-speed performance of the Ge PDis capable to convert these optical signals to electric signals thatmaintain the high data rate. The electric signals are outputted via thefirst electrode (as a cathode) and the second electrode (as an anode) tothe external electric circuit associated with a high-speed opto-electriccommunication network.

Optionally, the first/second metallic layer is formed by patterning asingle layer of metallic material, including typical conductor materialselected from copper, aluminum, tin, lead or others used in siliconphotonics devices. The patterning process leads to the formation of thefirst/second middle section out of a natural portion of the first/secondmetallic layer in a shape with a reducing width from the second noderegion with the expanded width to the first node region (of a smallerwidth). Similarly, the first/second trance line comprises a thinconductive line with a width of a few micrometers or less formed bypatterning a natural portion out of the first/second metallic layer.

Optionally, the method includes configuring the size, distance, andlocation of the third node region and sixth node region plus the secondintrinsic region in combination to effectively provide a capacitor witha capacitance value limited no greater than a few femto Faradays. Thesmall size of cathode and anode of the Silicon photodiode and thinfirst/second trace lines for connecting with external current/voltagesource are limiting factors of such small capacitance which is essentialfor not impacting the high-speed optical telecommunication designatedfor the Germanium photodiode.

Optionally, the method includes configuring the doping level of thesecond p-doped region and a second n-doped region and the size of thesecond intrinsic region to yield an ESD threshold of about ±100Vassociated with the Silicon photodiode. This almost increases the ESDthreshold by 2 times over the Germanium photodiode alone, providingenhanced ESD protection.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. An integrated photo detector with enhancedelectrostatic discharge damage (ESD) protection comprising: an inputwaveguide formed in a Si-on-insulator (SOI) substrate for receiving alight wave; a first photodiode formed in the SOI substrate and coupledto the input waveguide, the first photodiode being associated with afirst p-electrode and a first n-electrode; a second photodiode formed inthe SOI substrate associated with a second p-electrode and a secondn-electrode forming a capacitance no larger than a few femto Faradays; afirst electrode and a second electrode disposed respectively on the SOIsubstrate, the first/second electrode being respectively connected tothe first p/n-electrode via a first/second metallic layer patterned witha reduced width from the first/second electrode to the firstp/n-electrode and connected to the second p/n-electrode via afirst/second metallic wire.
 2. The integrated photo detector of claim 1,wherein the first photodiode is a Germanium-based photodiode configuredto detect the light wave modulated with a high data rate.
 3. Theintegrated photo detector of claim 1, wherein the input waveguidecomprise a material of silicon or germanium or silicon nitride formed inthe SOI substrate for transmitting the light wave therein.
 4. Theintegrated photo detector of claim 2, wherein the Germanium-basedphotodiode comprises a p-type Silicon base patterned within the SOIsubstrate and an intrinsic Germanium block formed overlying the p-typeSilicon base, the p-type Silicon base being partially implanted via afirst mask to form a first p++ doped region and the intrinsic Germaniumblock being partially implanted via a second mask to form a first n++doped region.
 5. The integrated photo detector of claim 4, wherein thefirst p-electrode is physically bounded onto the p++ doped region andthe first n-electrode is physically bounded onto the n++ doped region.6. The integrated photo detector of claim 1, wherein the secondphotodiode is a Silicon-based photodiode coupled to the Germanium-basedphotodiode to provide an electrostatic discharge damage threshold of±100V or higher.
 7. The integrated photo detector of claim 6, whereinthe Silicon-based photodiode comprises a p-type Silicon region joinedwith an n-type Silicon region patterned within the SOI substrate, thep-type Silicon region being partially implanted via a third mask to forma second p++ doped region and the n-type Silicon region being partiallyimplanted via a fourth mask to form a second n++ doped region.
 8. Theintegrated photo detector of claim 1, wherein each of the secondp-electrode and the second n-electrode is made substantially smaller insize than each of the first p-electrode and the first n-electrode. 9.The integrated photo detector of claim 2, wherein each of the firstelectrode and the second electrode is made substantially larger in sizeup to a few tens to hundreds of micrometers sufficient for forming asoldering connection with an external digital circuit for outputting anelectric signal converted by the Germanium-based photodiode.
 10. Theintegrated photo detector of claim 9 wherein the electric signalsubstantially maintains the high data rate of the light wave.
 11. Theintegrated photo detector of claim 1, wherein the first/secondp/n-electrode, the first/second electrode, the first/second metalliclayer, and the first/second metallic wire are substantially made from asingle metallic layer via a unified patterning process.
 12. Theintegrated photo detector of claim 1, wherein the first/second metallicwire comprises a substantially thin trace line of a few micrometers orless for minimizing the capacitance and sufficient to maintainelectrical connection between the first/second electrode and the secondp-type/n-type region.
 13. An integrated photo detector with enhancedelectrostatic discharge damage (ESD) protection comprising: a Germaniumphotodiode comprising an intrinsic Germanium layer formed on a p-typeSilicon base layer patterned within a Si-on-Insulator (SOI) substrate,the intrinsic Germanium layer comprising a first n++ doped region andthe p-type Silicon base layer comprising a first p++ doped region; aSilicon photodiode comprising a Silicon region patterned within the SOIsubstrate to form a p-type Silicon portion joined with a n-type Siliconportion, the p-type Silicon portion comprising a second p++ doped regionand the n-type Silicon portion comprising a second n++ doped region; afirst metallic layer being pattered to include a first p-electrodecoupled to the first p++ doped region, a second p-electrode coupled tothe second p++ doped region, a first electrode connected to the firstp-electrode by a portion of the first metallic layer with a reducingwidth and connected to the second p-electrode by a first trace line; asecond metallic layer being pattered to include a first n-electrodecoupled to the first n++ doped region, a second n-electrode coupled tothe second n++ doped region, a second electrode connected to the firstn-electrode by a portion of the second metallic layer with a reducingwidth and connected to the second n-electrode by a second trace line;wherein the Silicon photodiode is coupled with the Germanium photodiodeelectrically in parallel with a capacitance of no greater than a fewfemto Faradays and an enhanced ESD threshold of about ±100V.
 14. Amethod for manufacturing an integrated photo detector with improvedelectrostatic discharge damage (ESD) protection, the method comprising:forming a first Silicon base block and a second Silicon base block on asubstrate; forming a Germanium photodiode partially in the first Siliconbase block, the Germanium photodiode being associated with a firstp-electrode and a first n-electrode; forming a Silicon photodiode in thesecond Silicon bask block, the Silicon photodiode being associated witha second p-electrode and a second n-electrode, the second p-electrodeand the second n-electrode serving as two terminals of a capacitance nolarger than a few femto Faradays; forming a first electrode and a secondelectrode separately on the substrate; forming a first metallic layer onthe substrate, the first metallic layer being patterned to have a firstportion with a reducing width connecting the first electrode to thefirst p-electrode and a second portion with a first trace lineconnecting the first electrode to the second p-electrode; forming asecond metallic layer on the substrate, the second metallic layer beingpatterned to have a third portion with a reducing width to connect thesecond electrode to the first n-electrode and a fourth portion with asecond trace line to connect the second electrode to the secondn-electrode.
 15. The method of claim 14 wherein the first Silicon baseblock is a p-type Silicon layer and the second Silicon base blockcomprises a p-type Silicon portion joined with a n-type Silicon portion.16. The method of claim 15 wherein forming the Germanium photodiodecomprises depositing an intrinsic Germanium layer on the p-type Siliconlayer of the first Silicon base block; implanting a first n++ dopedregion in the intrinsic Germanium layer by masked implantation;implanting a first p++ doped region in the p-type Silicon layer;coupling the first n++ doped region to the first n-electrode; andcoupling the first p++ region to the first p-electrode.
 17. The methodof claim 15 wherein forming the Silicon photodiode comprises implantinga second p++ doped region in the p-type Silicon portion of the secondSilicon base block; implanting a second n++ doped region in the n-typeSilicon portion of the second Silicon base block; coupling the secondp++ doped region to the second p-electrode; and coupling the second n++doped region to the second n-electrode.
 18. The method of claim 14wherein the first/second metallic layer is configured to couple theSilicon photodiode to the Germanium photodiode electrically in parallelwith a characterized ESD threshold of about ±100V.
 19. The method ofclaim 18 further comprising forming an input waveguide on the substrateto couple with the Germanium photodiode for receiving a light wavemodulated with a high data rate.
 20. The method of claim 19 wherein thefirst/second electrode comprises a dimension of a few tens to hundredsof micrometers sufficient for forming a solder bump to connect with anexternal electronic circuit and output an electric signal generated bythe Germanium photodiode by detecting the light wave received from theinput waveguide.
 21. The method of claim 20 wherein the electric signalsubstantially maintains the high data rate of the light wave depended onmodulation.
 22. The method of claim 14 wherein the first/second traceline comprises a width of a few micrometers or less to minimize itsparasitic capacitance.
 23. The method of claim 14 wherein the substrateis a silicon-on-insulator substrate.